Conventional cotton harvesters include harvesting units commonly supported for vertical movement on a fore-and-aft wheeled frame of the harvester. Each harvesting unit includes a housing assembly defining a plant passage and a harvesting mechanism arranged within the housing. As the cotton harvester is driven across the cotton field, a row of cotton plants passes through the passage and the harvesting mechanism removes the cotton therefrom.
Cotton grows substantially along the entire height of the cotton plant. At the lower end, the cotton grows barely off the ground and sometimes on the ground. The harvesting units, therefor, follow as close to the ground as possible so as to pick all of the cotton from the plant.
The ground over which the harvester is driven is usually uneven. Accordingly, if the harvesting unit is set for a lowermost depression on the ground, the stalk lifters extending from a forward end of the harvesting unit will tend to "dig into" high points on the ground contour. As the harvester is driven across the field, the wheels on the harvester frame ride between adjacent rows of cotton plants. In softer muddy conditions, the wheels of the harvester deform the field into slight recesses or valleys and raised ridges. As will be appreciated, proper positioning of the harvesting unit relative to the ground contour is further more complicated in such undulating field conditions.
To optimize efficiency during the harvesting operation, cotton harvesters are known to include a harvesting unit height adjusting system for automatically controlling the height of the harvesting unit relative to the ground. The elevation of the harvesting unit is primarily controlled by a lift mechanism actuated in accordance with ground contours. Variations of the ground contour are sensed by a ground engaging element, such as a shoe, mounted on the harvesting unit in a manner to press on the ground and be positionally displaced in response to variations of the ground contour profile. The sensing shoe of the height adjustment system is connected as by a linkage assembly to a control valve of a hydraulic system connected to the lift mechanism. The control valve controls operation of the lift mechanism and thereby elevation of the harvesting units.
The shoe or sensing element of the height adjustment system defines a ground engaging surface extending generally parallel to a flat ground surface. As the harvester is driven across the field, the sensing shoe moves over and is in contact with the ground. As will be appreciated, a lateral edge of the sensing shoe tends to "dig into" the sides of raised ridges in the cotton fields. The abrasiveness of the ground surface contact coupled with the weight of a linkage mechanism connected thereto and the concentrated contact with the ground causes the ground engaging lateral edge of the shoe to quickly wear resulting in attendant and undesirable consequences.